Hi Joseph, I understand your logic. I guess it's just a difference in what we consider more intuitive. I think in terms of ascending order, so lowest (in value) to highest. Also I wanted it to keep the same logic for the usual colormaps in MATLAB. If I already had a colormap, and I wanted to "vivid-ify" it, I may want to do:

cm = colormap;
colormap(vivid(cm));

But this would flip it.

By the way, I have highlighted this entry on this week's Pick of the Week:
http://blogs.mathworks.com/pick/2011/12/09/a-vivid-colormap/

@Jiro, thank you. In regards to your example, it is not a bug if it was intentional. :o) I thought it was more intuitive to input colors top-to-bottom so that if inputs are provided in a "rainbow order", users would not have to think about the color sequence in reverse. For example:
>> colormap(vivid('royg'));
would have red on top and green on the bottom, which I thought made more sense than:
>> colormap(vivid('gyor'))

However, if you do not like this feature, you can replace line 136 with the following:
>> rgb = repmat(reshape(clrs,1,nc,3),ns,1);
...where I just removed the call to flipud.